There's little controversy about the benefits of breastfeeding infants over giving them formula. Mother's milk is the perfect food, providing exactly the correct nourishment for newborns, while protecting them from many illnesses.

There also are good economic and maternal health reasons that would seem to make a compelling case for breastfeeding for the six-to-12 months recommended by the American Academy of Pediatrics.

"However one major reason why women stop breastfeeding is low weight gain and growth rate of their baby," Steven L. Bealer of the University of Utah points out. His team of researchers decided to find out what factors might cause low weight gain.

They studied how blocking the oxytocin (OT) hormonal system, which serves several functions in the birth process and milk delivery during nursing (lactation), would affect offspring during and after birth. They found that if the central OT receptors in the pregnant females' brain are blocked during pregnancy, then their offspring's growth was reduced from the third day after birth through the two-week experiment.

Interestingly, the actual delivery itself wasn't affected nor was the number of "pups" in each litter. Even the delivery weights of the test females' offspring was the same as "control dams" pups' delivery weights.

A blocked OT system reduces post-natal weight gains

However what they did find was that in the mothers with blocked OT systems, the initial release of OT following the onset of pups suckling was significantly delayed compared to untreated females. "Finally, litter weight gain during a three-hour suckling period was significantly smaller in pups nursing dams that were treated with OT receptor blocker during gestation," Bealer reports.

"What we learned is that OT receptor stimulation during gestation is necessary for normal OT responsiveness and consequently for normal pup development during lactation," Bealer notes. "More efficient and longer lasting breastfeeding results in better human health throughout life," he adds, "so if the efficiency of the oxytocin system can be improved, perhaps it will encourage mothers to lengthen how long they breast feed their children."